Why do parents refuse their girls to wear makeup? Even a little bit?

because now that i'm 21 and wearing a full face of makeup, i wish i had listened to my mum :)
also guys prefer girls without makeup
makeup is expensive
takes up a lot of time
not good for your skin can make spots worse

Could be reasons like religion. Most of the time they just don't want to see there little girl growing up so fast. They want you to be they're little girl forever.

Could be several reasons. They come from a culture or religion that believes in no makeup for any female. Or they think their daughter is too young for makeup (If the mom wears makeup, then this would be what's happening.) Or the girl wants to wear too much makeup like heavy winged eyeliner or super bright heavy eyeshadow, etc. They might think it's just easier to say no to any makeup. Or, they don't want to think of their daughter as growing up.

Could be any of those reasons but if it's the cultural/religious reason, then you won't change their minds probably. You could still pluck your brows and maybe get permission to wear a tinted lip balm by stressing that it's for chapped lips instead of like makeup. You might also get them to let you wear skin colored creams for breakouts if you have those. If not, then that reasoning won't work. Good luck...

The two main reasons girls wear makeup are because they don't like the way they look without it or because they believe it makes them look older and sexier to other people. A good mom encourages her daughter to love herself the way she is, and if people don't find that good enough, those people aren't worth having as friends.

Reasons:
- some are too young
- makeup is bad for your skin
- clogs up your pores and may cause further damage
- hard to wash off sometimes
- it looks bad if you use too much
- think they look better au naturel
- don't want their daughters to age or mature that fast

Probably several reasons, and different ones for different people. If I had a daughter, I would probably let her wear a little mascara and light lip gloss when she was about 14, but not foundation or eye shadow, i.e., the whole works, until at least 15. That is, unless she had acne and wanted to cover up the awful breakouts and redness, which can give you a terrible complex. If that were the case, I would take her to a dermatologist and have her follow a good cleaning regimen and find a foundation that was light and not bad for the skin, just enough to cover up the embarrassment of the acne, which I experienced myself as a kid. Kids grow up way too fast these days, and believe me, makeup is WORK! Stay young for as long as you can!

Parents know our beauty so they think there's no need to wear any makeup

Because they think their girls will attract the wrong sort of attention. Or apply the makeup messily and look like street tramps. Or cake it on and end up with acne. Some, it is their culture or religion to eschew makeup.

I understand this because girls of 12 and 13 are wayyyy to young to wear makeup ._. it could ruin their faces :(

Because once you start you don't stop. You only add to the routine.
Plus, the chemicals in makeup (particularly face makeup) isn't good for the skin.
So the later you start the better.